Surface and thermodynamic properties of four synthetic anionic surfactants are studied. The properties of these surfactants are correlated with their flotation performance to upgrade a petroleum coke sample to minimize its impurities. The surfactants are isomers for dodecylbenzenesulfonate of the same molecular weight, but the benzene ring is attached to different carbon atoms along the dodecyl chain. The results show that the position of benzene ring, attached to the carbon chain, affects their surface and thermodynamic properties. The values of critical micelle concentration (cmc), minimum area per molecule (A(min)), effectiveness (Pi(cmc)) and efficiency (pC(20)), to reduce surface tension of water, are decreased with changing the position of benzene ring from carbon atom number 3 to 5. Increasing temperature is accompanied by an increase in each of cmc, minimum area per molecule (A(min)), Gibbs energy of micellization (Delta G(mic)(o)), and adsorption (Delta G(ad)(o)). Meanwhile, the values of surface tension (gamma(cmc)) at cmc, surface excess concentration (Gamma(max)), and effectiveness (Pi(cmc)) to reduce surface tension of water are decreased. There is a good relationship between the structure of a surfactant and its efficiency as a collector. Changing the position of the phenyl group along the alkyl chain of a surfactant toward its central carbon atom (6 phi C12) improves its efficiency as a collector.